The present invention relates to an optical fiber positioning member used for optically coupling optical fibers to each other.
For connecting optical fibers to each other in the optical communication, an optical connector is usually employed, whereas optical fiber positioning members such as a ferrule and a sleeve are used in the optical connector. These optical fiber positioning members are required to have a high dimensional precision for positioning the axial centers of optical fibers with respect to each other with a high accuracy, and also to have a high dimensional stability when they are to be used over a long period of time. At the same time, since the optical fiber positioning members are repeatedly attached and detached, they require not only a sufficient mechanical strength but also a long-term durability.
Meanwhile, as optical fiber positioning members in optical connectors, ferrules made of zirconia and the like have conventionally been known. Also, ferrules in which optical fiber positioning members are obtained by transfer-molding an epoxy resin, which is a thermosetting resin, have been known. However, the ferrules made of zirconia are less advantageous than ferrules made of plastics in terms of cost, whereas it takes time for ferrules molded of thermosetting resins to cure at the time of molding, thereby lowering their productivity.
Hence, the use of thermoplastic resins which yield favorable productivity and are inexpensive has been under consideration. Known thermoplastic resins, however, are problematic in that their injection pressure at the time of molding is high, their shrinkage is large, and so forth, whereby it is not easy for practical high-precision ferrules to be obtained therefrom. Under such circumstances, techniques yielding practical ferrules have recently been reported. For example, Japanese Patent Application Laid-Open No. HEI 5-345328 discloses a ferrule in which a resin composition mainly composed of a polyphenylene sulfide resin is filled with silica particles having an indefinite or spherical form.
Also, Domestic Republication of PCT International Publication WO95/25770 discloses a ferrule in which a resin composition containing a polyphenylene sulfide resin or the like at a ratio in the range of 20% to 40% by weight is filled with spherical fine silica particles or the like at a ratio in the range of 40% to 60% by weight, and whiskers such as potassium titanate whiskers, aluminum borate whiskers, silicon carbide whiskers, silicon nitride whiskers, zinc oxide whiskers, alumina whiskers, graphite whiskers, or the like.
As a result of diligent studies concerning the conventional ferrules mentioned above, the inventors have found that, though the above-mentioned ferrules are advantageous in their dimensional precision and dimensional stability since the silica particles and/or whiskers are contained in the resin composition, they have problems as follows.
Namely, in the ferrule in which a resin composition is filled with silica particles, the aspect ratios of silica particles are small, whereby their reinforcing effect is insufficient. As a consequence, in an MT optical connector of a type using a guide pin, the strength of the ferrule around the guide hole for inserting the guide pin may become so weak that a part of the ferrule around the guide hole may chip off when ferrules are connected to each other by means of a clip. In particular, when a high-speed automatic switching apparatus for mechanically connecting MT optical connectors at a high speed is employed, the ferrules are prone to damage.
Also, in the ferrule in which a resin composition containing a polyphenylene sulfide resin or the like is filled with spherical fine particles and whiskers, the strength of the ferrule around the guide hole for inserting a guide pin may not be sufficient, thus causing a part of the ferrule to chip off around the guide hole when the guide pin is inserted into or pulled out from the guide hole. In an MPO optical connector of a push-on/pull-off type, in particular, since a guide pin may be inserted into the guide hole of the ferrule in an impacting fashion while being shifted or tilted, peripheral portions of the guide hole of the ferrule are apt to chip off. As a consequence, the ferrule may necessitate replacement or the like at a relatively early stage, and may not endure a long-term use.
In view of the foregoing circumstances, it is an object of the present invention to provide an optical fiber positioning member having practically sufficient mechanical strength and long-term durability while maintaining high dimensional precision and dimensional stability.
As a result of diligent studies for achieving the above-mentioned object, the inventors have found that, when a resin composition containing a polyphenylene sulfide resin further contains a specific amount of whiskers made of a specific material in addition to silica particles, the mechanical strength of the optical fiber positioning member can be improved in particular, which is advantageous in terms of long-term durability, thus accomplishing the present invention.
Namely, the optical fiber positioning member in accordance with the present invention comprises a resin composition containing a polyphenylene sulfide resin at a ratio in the range of 15% to 35% by weight, silica particles at a ratio in the range of 45% to 65% by weight, and silicate whiskers at a ratio in the range of 26% to 35% by weight, the resin composition containing the silica particles and the silicate whiskers at a ratio in the range of 65% to 85% by weight.
In the optical fiber positioning member of the present invention, as the silicate whiskers are contained in the resin composition, the mechanical strength becomes higher than that in the cases where other kinds of whiskers are contained therein. However, the mechanical strength of the optical fiber positioning member will be insufficient if the silicate whisker content is less than 26% by weight, whereas anisotropy will occur and thereby the dimensional precision will lower if the content exceeds 35% by weight. The moldability will deteriorate and the dimensional precision will lower if the polyphenylene sulfide resin content is less than 15% by weight, whereas the reinforcing effects of silica particles, whiskers, and the like upon the polyphenylene sulfide resin will be so small that the mechanical strength of the optical fiber positioning member will lower if the content exceeds 35% by weight. Also, the coefficient of linear expansion and anisotropy will become so high that the dimensional precision will lower if the silica particle content is less than 45% by weight; whereas the dimensional precision will lower if the silica particle content exceeds 65% by weight, since the fluidity of the resin composition at the time of molding decreases and thereby deteriorates the moldability. Also, since the ratio of polyphenylene sulfide resin decreases, the optical fiber positioning member becomes brittle. Further, the dimensional precision of the optical fiber positioning member will lower if the total content of the silica particles and silicate whiskers is less than 65% by weight; whereas, if the total content exceeds 85% by weight, the fluidity of the resin composition at the time of molding will worsen, so as to deteriorate the moldability, thereby lowering the dimensional precision, and the mechanical strength will be insufficient.
Also, the optical fiber positioning member of the present invention comprises a resin composition containing a polyphenylene sulfide resin, silica particles, and a plurality of kinds of whiskers, the resin composition containing the silica particles and the whiskers at a ratio in the range of 65% to 85% by weight.
In the optical fiber positioning member of the present invention, as a plurality of kinds of whiskers are used, the whiskers having different forms and ingredients would be mixed together. As a consequence, the anisotropy of the resin composition is canceled, whereby the dimensional precision would improve. Also, in the optical fiber positioning member of the present invention, the dimensional precision of the optical fiber positioning member will lower if the total content of the silica particles and whiskers is less than 65% by weight; whereas, if the total content exceeds 85% by weight, the fluidity of the resin composition at the time of molding will worsen, so as to deteriorate the moldability, thereby lowering the dimensional precision, and the mechanical strength will be insufficient.
Further, the optical fiber positioning member of the present invention comprises a resin composition containing a polyphenylene sulfide resin mainly composed of a linear type polyphenylene sulfide resin at a ratio in the range of 22% to 35% by weight, silica particles at a ratio in the range of 45% to 65% by weight, and silicate whiskers at a ratio in the range of 3% to 13% by weight, the resin composition containing the silica particles and the silicate whiskers at a ratio in the range of 58% to 78% by weight.
In the optical fiber positioning member of the present invention, as the linear type polyphenylene sulfide resin is used as a main ingredient of the polyphenylene sulfide resin, the molecular weight of the polyphenylene sulfide resin increases, thereby further enhancing the mechanical strength of the optical fiber positioning member. The moldability will worsen and the dimensional precision will lower if the polyphenylene sulfide resin content in the resin composition is less than 22% by weight, whereas the reinforcing effects of silica particles, whiskers, and the like upon the polyphenylene sulfide resin will be so small that the mechanical strength of the optical fiber positioning member will lower if the content exceeds 35% by weight. Also, the coefficient of linear expansion and anisotropy will become so high that the dimensional precision will lower if the silica particle content is less than 45% by weight; whereas the dimensional precision will lower if the silica particle content exceeds 65% by weight, since the fluidity of the resin composition at the time of molding decreases and thereby deteriorates the moldability. Also, since the ratio of polyphenylene sulfide resin decreases, the optical fiber positioning member becomes brittle. The reinforcing effects due to the silicate whiskers will be small and the mechanical strength will lower if the silicate whisker content in the resin composition is less than 3% by weight; whereas, if the content exceeds 13% by weight, the silicate whiskers will increase and, since polyphenylene sulfide contains the linear type polyphenylene sulfide resin, which is a high molecular weight ingredient, the fluidity of the resin composition at the time of molding will lower, thereby decreasing the dimensional precision and the mechanical strength. Also, the dimensional precision of the optical fiber positioning member will lower if the total content of the silica particles and silicate whiskers is less than 58% by weight; whereas, if the total content exceeds 78% by weight, the fluidity of the resin composition at the time of molding will worsen, so as to deteriorate the moldability, thereby lowering the dimensional precision, and the mechanical strength will be insufficient.